1. Field of the Invention
The present invention relates to an electronic apparatus such as a one-chip microcomputer incorporation in electronic devices, for example.
2. Description of the Prior Art
One-chip microcomputers incorporated in electronic devices are constructed by electronic apparatus in which a fixed memory means (ROM), a processing means (CPU), an input means, a variable memory means (RAM), etc., are unitarily integrated.
In such an electronic apparatus (one-chip microcomputer), a processing program for the processing means (CPU) is stored in the fixed memory means (ROM). That is, a particular processing is carried out in accordance with an information (processing program) stored in the fixed memory means (ROM). Therefore, if this fixed memory means (ROM) is formed by a mask ROM, then such electronic apparatus can be mass-produced inexpensively.
The above electronic apparatus are incorporated in electronic devices such as a consumer video tape recorder having a built-in camera, a small video deck or the like. Recently, electronic apparatus have been designed to have multiple functions in order to discriminate products. As a result, the amount of information (processing program) stored in the fixed memory means (ROM) is increased. In particular, as the size of the processing program is increased considerably, the occurrence of bug therein cannot be avoided.
If such bug is discovered after the electronic apparatus has been mass-produced, the mass-produced apparatus must be abandoned or mass-produced one more time. Further, external parts for patching the bug must be added to the electronic apparatus. If electronic apparatus are mass-produced one more time, then a lot of additional costs become necessary. Furthermore, external parts cannot be substantially mounted on electronic devices because the electronic device has many electronic parts mounted therein with high density.
To solve the above problems, the assignee of the present application has previously proposed a means that can correct such bug after electronic devices have been mass-produced (see Japanese Patent Application No. 3-118799). To be more concrete, according to this previously-proposed means, an electronic device includes therein a patch information memory means for patching a bug and an access change-over means. Then, a defective or bug portion of the information stored in the fixed memory means is identified and the access is changed over from the fixed means to the patch information memory means at that defective or bug portion.
In this previously-proposed means, however, the design of the electronic device itself (hardware) must be changed such as when there are provided the patch information memory means and the access change-over means. Therefore, this previously-proposed means cannot be applied to the existing electronic devices with ease.